Colloidal silver-based lateral flow immunoassay for rapid detection of melamine in milk and animal feed

An immunosilver chromatographic strip based on a monoclonal antibody was developed for the detection of melamine (MEL) residues in milk and animal feed. Colloidal silver nanoparticles (AgNPs), of a diameter of approximately 10.4 nm, were surface-modified with trisodium citrate dehydrate (TSC) in order to improve their stability and dispersion. The anti-MEL monoclonal antibody (mAb) was successfully immobilized on the surface of AgNPs by ionic interactions and characterized using XRD, UV–Vis, TEM and XPS analyses. Surface modification of Ag-mAb conjugates with varying cross-reactivity and thermo-stability was employed to design and prepare labels for use in a lateral flow immunoassay (LFIA) to examine whether these factors affect the performance of the assay. The results showed that no cross-reactions with homologues cyanuric acid, ammeline or ammelide were found, and the test strip remained stable after storage for one year at room temperature. Under optimized conditions, a detection limit of 0.30 ppm for standard melamine was achieved, and limits of detection of 0.750 ppm and 0.875 ppm were obtained in milk and animal feed, respectively.